NATURE OF PLANTS 125 



number of more or less elongated cells, the so-called suspensor, 

 and a terminal cell or embryo cell (Fig. 81, B, V). In the 

 meantime the endosperm cell has divided again and again and 

 the resulting naked nuclei have become arranged around the 

 sides of the embryo sac (Fig. 81, B, en}. This formation of 

 endosperm cells continues until they more or less fill the embryo 

 sac and they also become surrounded with cell walls. These 

 endosperm cells are filled with food and serve to nourish the 

 germinating gametospore just as the nucellus nourished the 

 female gametophyte. While the suspensory cells usually soon 

 cease to grow, the embryo cell divides very actively, as shown 

 in Fig. 81, C-E, and soon there is a clear indication of a minute 

 plant with root, stem and leaves (Fig. 81, F). This minute 

 plant developed by the germination of the gametospore, is called 

 the embryo. In the case of the plant under consideration the 

 embryo, when fully formed consists of a stem with two laterally 

 placed leaves, the cotyledons, and a root. The region of the 

 stem above the attachment of the cotyledons is known as the 

 plumule and frequently assumes the form of a minute bud. The 

 region of the stem below the cotyledons is termed the hypocotyl 

 and the root and root cap appear at its lower end (Fig. 82, A). 

 The ovule containing the mature embryo is called a seed. The 

 interesting feature about the seed is the fact that it is a structure 

 in which growth has ceased and that it is capable, owing to a 

 remarkable series of devices that will be noted directly, of re- 

 maining in this condition, i. e., dormant often for one or more 

 years. 



Great variation characterizes the germination of the gameto- 

 spore in the different groups of plants, but the development out- 

 lined above is fairly characteristic of those plants that form an 

 embryo with two cotyledons. Such plants are called for this 

 reason dicotyledons. Other plants develop an embryo with but 

 one cotyledon, as our grasses, lilies, etc., and for this reason they 

 are called monocotyledons. Further variations will be seen in 

 cone-bearing trees, ferns, etc. 



It must be borne in mind that the formation of the seed is 

 also attended with profound changes in the structure of the 



